Iambus means: A foot consisting of a short syllable followed by a long
one, as in /mans, or of an unaccented syllable followed by an accented
one, as invent; an iambic. See the Couplet under Iambic, n.

Zymogen means: A mother substance, or antecedent, of an enzyme or
chemical ferment; -- applied to such substances as, not being
themselves actual ferments, may by internal changes give rise to a
ferment.